Bulk acoustic wave resonator

ABSTRACT

Disclosed is a bulk acoustic wave resonator (BAWR). The BAWR includes a bulk acoustic wave resonance unit with a first electrode, a second electrode, and a piezoelectric layer. The piezoelectric layer is disposed between the first electrode and the second electrode. An air edge is formed at a distance from a center of the bulk acoustic wave resonance unit.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.13/691,114 filed on Nov. 30, 2012, which claims the benefit under 35U.S.C. §119(a) of Korean Patent Application No. 10-2011-0127686, filedon Dec. 1, 2011, in the Korean Intellectual Property Office, the entiredisclosure of which is incorporated herein by reference for allpurposes.

BACKGROUND

1. Field

The following description relates to a bulk acoustic wave resonator(BAWR).

2. Description of Related Art

A bulk acoustic wave resonator (BAWR) operates by the application of anelectric potential to electrodes that are disposed on and/or below apiezoelectric layer. The piezoelectric layer oscillates in response to ahigh frequency electric potential applied to the electrodes. As aresult, the BAWR operates.

Bandwidth of the BAWR is proportional to an Acousto-electric couplingcoefficient. A film characteristic of the electrodes and thepiezoelectric layer affect the Acousto-electric coupling coefficient.Therefore, to increase the bandwidth of the BAWR, it is necessary toincrease a value of the Acousto-electric coupling coefficient.

Accordingly, it is necessary to continuously develop technologies thatimprove bandwidth using the film characteristic of the electrodes andthe piezoelectric layer.

SUMMARY

In one general aspect, there is provided a bulk acoustic wave resonator(BAWR), including a bulk acoustic wave resonance unit including a firstelectrode, a second electrode, and a piezoelectric layer disposedbetween the first electrode and the second electrode, and an air edgeformed at a predetermined distance from a center of the bulk acousticwave resonance unit.

The air edge may be formed by etching a predetermined portion of an edgeof the bulk acoustic wave resonance unit about as thick as the bulkacoustic wave resonance unit in a vertical direction.

The BAWR may further include an air gap, disposed below the bulkacoustic wave resonance unit and on a substrate that reflects a verticalacoustic wave generated from the bulk acoustic wave resonance unit.

The air edge may be formed by penetrating a predetermined portion of anedge of the bulk acoustic wave resonance unit up to the air gap in avertical direction.

The air edge may be formed by enlarging a via-hole disposed on the bulkacoustic wave resonance unit.

The first electrode, the second electrode, and the piezoelectric layermay be etched in the same process by application of a photo-mask layeredon a portion different from an edge of the bulk acoustic wave resonanceunit so that the air edge may have a steep slope.

The air edge may be formed on a portion of an edge of the bulk acousticwave resonance unit, the portion being greater than or equal to 20% ofthe edge.

The BAWR may further include a bridge, disposed on a predetermined areaexcluding a portion where the air edge is formed in an edge of the bulkacoustic wave resonance unit, that supports the bulk acoustic waveresonance unit.

The BAWR may further include a passivation layer, formed of one of asilicon oxide-based material, a silicon nitride-based material, and analuminum nitride (AlN)-based material, disposed on or below thepiezoelectric layer.

The BAWR may further include a passivation layer, formed of one of asilicon oxide-based material, a silicon nitride-based material, and anAlN-based material, disposed on or below the first electrode.

The BAWR may further include a passivation layer, formed of one of asilicon oxide-based material, a silicon nitride-based material, and anAlN-based material, disposed on or below the second electrode. The bulkacoustic wave resonance unit may include a first frame formed by locallyforming, though evaporation, an additional film at a portion that isconnected to the first electrode and excludes the air edge on an edge ofthe bulk acoustic wave resonance unit, and a second frame formed bylocally forming, through evaporation, an additional film at a portionthat is connected to the second electrode and excludes the air edge onthe edge of the bulk acoustic wave resonance unit.

The bulk acoustic wave resonance unit may include a first frame formed,though local etching, at a portion that is connected to the firstelectrode and excludes the air edge on an edge of the bulk acoustic waveresonance unit, and a second frame formed, through local etching, at aportion that is connected to the second electrode and excludes the airedge on the edge of the bulk acoustic wave resonance unit.

The first electrode may include a portion connected to a predeterminedportion of an edge of the bulk acoustic wave resonance unit, in a formof a finger, and a portion exposed to the air edge through patterning.

The second electrode may include a portion connected to a predeterminedportion of an edge of the bulk acoustic wave resonance unit, in a formof a finger, and a portion exposed to the air edge through patterning.

The bulk acoustic wave resonance unit may include a first frame formedby locally forming, through evaporation, an additional film at a portionwhere the first electrode is connected, in a form of a finger, to apredetermined portion of an edge of the bulk acoustic wave resonanceunit, and a second frame formed by locally forming, through evaporation,an additional film at a portion where the second electrode is connected,in a form of a finger, to a predetermined portion of the edge of thebulk acoustic wave resonance unit.

The bulk acoustic wave resonance unit may include a first frame formed,through local etching, at a portion where the first electrode isconnected, in a form of a finger, to a predetermined portion of an edgeof the bulk acoustic wave resonance unit, and a second frame formed,through local etching, at a portion where the second electrode isconnected, in a form of a finger, to a predetermined portion of the edgeof the bulk acoustic wave resonance unit.

In another general aspect, there is provided a BAWR, including asubstrate, an air gap disposed on a predetermined area of the substrate,a first electrode disposed on the air gap, a piezoelectric layerdisposed on the first electrode, a second electrode disposed on thepiezoelectric layer, and an air edge formed at a predetermined distancefrom a center of the air gap.

The air edge may be formed by etching a predetermined portion of an edgeof a portion where the first electrode, the piezoelectric layer, and thesecond electrode are layered as thick as the first electrode, thepiezoelectric layer, and the second electrode in a vertical direction.

In yet another general aspect, a method of manufacturing a bulk acousticwave resonance unit includes the steps of: forming a first electrode;forming a second electrode; forming a piezoelectric layer between thefirst and the second electrode; and forming an air edge at apredetermined distance from a center of the bulk acoustic wave resonanceunit.

The air edge is formed by etching a predetermined portion of an edge ofthe bulk acoustic wave resonance unit about as thick as the bulkacoustic wave resonance unit in a vertical direction.

The air edge is formed by penetrating a predetermined portion of an edgeof the bulk acoustic wave resonance unit in a vertical direction.

The air edge is formed by enlarging a via-hole disposed on the bulkacoustic wave resonance unit.

An illustrative example provides a BAWR that uses an air edge to reduceloss due to a horizontal acoustic wave and thus, may improve anAcousto-electric coupling coefficient.

An illustrative example provides a BAWR that uses an air edge to reduceloss due to a horizontal acoustic wave and thus, the BAWR may have ahigh Q-factor value.

An illustrative example may secure a high Acousto-electric couplingcoefficient using a BAWR and thus, may embody an RF filter or an RFduplexer having a wide bandwidth.

An illustrative example embodies an RF duplexer having a narrow band gapusing a BAWR.

An illustrative example provides a BAWR that operates as a referenceresonator of an oscillator and thus, may remove phase noise.

Companies operating a mobile communication system, for example, aportable phone, suffer huge costs for the allocation of frequencies tobe used for communication because of the limited number of frequencyresources.

To prevent interference from occurring among transmitted and receivedsignals, a predetermined band gap is needed between a transmissionfrequency and reception frequency of a terminal.

Thus, companies have tried to reduce the band gap between thetransmission frequency and the reception frequency in order toeffectively utilize the allocated frequencies.

In addition, the BAWR may be used for input and output of wireless dataas a filter, a transmitter, a receiver, or a duplexer in a wirelesscommunication device.

There are various types of wireless communication devices for variouspurposes, and the number of wireless devices, conventionally regarded aswired devices, has increased rapidly.

Thus, a number of fields to which the BAWR may be applied has expanded.

Other features and aspects may be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a cross-sectional view of a bulkacoustic wave resonator (BAWR) in accordance with an illustrativeexample.

FIG. 2 is a diagram illustrating a top view a BAWR in accordance with anillustrative example.

FIGS. 3A and 3B are diagrams illustrating a top view and across-sectional view of a BAWR in accordance with an illustrativeexample.

FIGS. 4A through 4C are diagrams illustrating a top view andcross-sectional views of a BAWR in accordance with an illustrativeexample.

FIG. 5 is a diagram illustrating a top view of a BAWR in accordance withan illustrative example.

FIGS. 6A through 6C are diagrams illustrating a top view and sectionalviews of a BAWR in accordance with an illustrative example.

FIGS. 7A through 7C are diagrams illustrating a top view and sectionalviews of a BAWR in accordance with an illustrative example.

FIG. 8 is a flow chart illustrating a method of manufacturing a BAWRunit in accordance with an illustrative example.

Throughout the drawings and the detailed description, unless otherwisedescribed, the same drawing reference numerals will be understood torefer to the same elements, features, and structures. The relative sizeand depiction of these elements may be exaggerated for clarity,illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses and/orsystems described herein. Accordingly, various changes, modifications,and equivalents of the systems, apparatuses and/or methods describedherein will be suggested to those of ordinary skill in the art. Thesequence(s) of processing steps and/or operations described areexamples; however, the sequence of and/or operations are not limited tothat which is set forth herein and may be changed as is appreciated bythose of ordinary skill in the art, with the exception of steps and/oroperations necessarily occurring in a certain order. Also, descriptionsof well-known features and operations are omitted for increased clarityand conciseness.

A resonator having a high Q value is required to reduce the band gap ina radio frequency (RF) communication system. Furthermore bandwidth needsto be increased to satisfy amount and rate of data transmission whichare gradually increasing.

A bulk acoustic wave resonator (BAWR) is a device that induces aresonance using a vertical acoustic wave to electrically utilize theresonance. The BAWR uses an air gap structure as a reflector to minimizethe loss of the vertical acoustic wave, or the BAWR uses a reflectorstructure corresponding to a plurality of alternately evaporatedreflection films.

However, because of film characteristics of a film included in the BAWR,a horizontal acoustic wave might also exist in addition to a verticalacoustic wave. When the horizontal acoustic wave is transferred to anexternal side of the BAWR, the loss of the horizontal acoustic wavecould occur and the Q value of the BAWR could decrease.

The BAWR may be raised commensurate with a thickness of an air gap,above a substrate through the air gap to improve a reflectioncharacteristic of an acoustic wave. When the BAWR has a frequencyband-pass characteristic, a plurality of resonators are disposed on aplane and the resonators may be connected to a common electrode, toimprove a reflection characteristic or transmission characteristicwithin a frequency band range.

An Acousto-electric coupling coefficient is proportional to a band gapbetween a resonant frequency and an anti-resonant frequency.Accordingly, a value of the Acousto-electric coupling coefficient may beincreased by changing the resonant frequency or the anti-resonantfrequency. The BAWR may adjust the band gap between the resonantfrequency and the anti-resonant frequency by reflecting a horizontalacoustic wave using an air edge.

Thus, the BAWR may reflect a horizontal acoustic wave using an air edge,may increase a value of an Acousto-electric coupling coefficient, andmay increase bandwidth.

FIG. 1 illustrates a cross-sectional view of an example of a BAWR inaccordance with an illustrative example.

Referring to FIG. 1, the BAWR includes a bulk acoustic wave resonanceunit 110, an air edge 120, and an air edge 130.

The bulk acoustic wave resonance unit 110 includes a first electrode115, a piezoelectric layer 113, and a second electrode 111. Thepiezoelectric layer 113 is disposed between the first electrode 115 andthe second electrode 111. The first electrode 115 or the secondelectrode 111 is formed of a material, for example, molybdenum (Mo),ruthenium (Ru), aluminum (Al), platinum (Pt), titanium (Ti), tungsten(W), palladium (Pd), chromium (Cr), nickel (Ni), and other suitablematerials.

The bulk acoustic wave resonance unit 110 generates a resonant frequencyand an anti-resonant frequency through the piezoelectric layer 113,based on a signal applied to the first electrode 115 and the secondelectrode 111.

The bulk acoustic wave resonance unit 110 uses an acoustic wavegenerated from a piezoelectric material. When an RF signal is applied tothe piezoelectric material, mechanical oscillations occur and anacoustic wave is generated. Examples of the piezoelectric material mayinclude zinc oxide (ZnO), aluminum nitride (AlN), and other suitablematerials.

Resonance occurs when half of a wavelength of the applied RF signal isequal to a thickness of a piezoelectric film. When resonance occurs, anelectrical impedance of the BAWR is sharply changed and thus, the BAWRmay be utilized as a filter to select a frequency.

A resonant frequency may be determined based on a thickness of apiezoelectric film, an electrode surrounding the piezoelectric film, andan intrinsic acoustic wave speed of the piezoelectric film, by way ofnon-limiting example. For example, resonant frequency may increase asthe thickness of the piezoelectric film decreases.

The resonant frequency may be a frequency occurring when a response toan applied signal is greatest. Impedance of the BAWR at the resonantfrequency is thus minimal. The anti-resonant frequency may be afrequency occurring when a response to an applied signal is lowest.Impedance of the BAWR at the anti-resonant frequency is thus maximal.

The bulk acoustic wave resonance unit 110 may be disposed on an air gap140. A reflection characteristic of a vertical acoustic wave generatedfrom the bulk acoustic wave resonance unit 110 may be improved throughthe inclusion of the air gap 140. The air gap 140 may be formed inside asubstrate 160, through etching, or may be formed on the substrate 160using a sacrificial layer (not shown) patterned to correspond to a shapeof the air gap 140.

The substrate 160 may be formed of silicon or poly-silicon having a highresistance, by way of non-limiting example. A passivation layer 150 maybe layered on the substrate 160 to prevent damage to the substrate 160during a process of generating the air gap 140. The passivation layer150 may be formed of one of a silicon oxide-based material, a siliconnitride-based material, and an aluminum nitride-based material.

The air edge 120 and the air edge 130 may be formed at a predetermineddistance from a center of the bulk acoustic wave resonance unit 110. Theair edge 120 and the air edge 130 may be formed at a predetermineddistance from a center of the air gap 140.

The air edge 120 and the air edge 130 may be formed by enlargingvia-holes (not shown) used for forming the air gap 140. The air gap 140may be formed by removing the sacrificial layer using xenon difluoride(XeF₂) gas or other suitable materials injected through the via-hole.The via-hole may be formed on a predetermined area of the bulk acousticwave resonance unit 110.

A vertical acoustic wave generated from the bulk acoustic wave resonanceunit 110 may be reflected by the air gap 140 to prevent loss due to ahorizontal acoustic wave and or a vertical acoustic wave in thesubstrate 160 and thus, may remain in the bulk acoustic wave resonanceunit 110. A horizontal acoustic wave generated from the bulk acousticwave resonance unit 110 may be reflected by the air edge 120 and the airedge 130 to prevent loss due to a horizontal acoustic wave and or avertical acoustic wave in the piezoelectric layer 113 and thus, mayremain in the bulk acoustic wave resonance unit 110.

Since loss in the vertical acoustic wave and the horizontal acousticwave does not occur, the BAWR may have a high Q value, a highAcousto-electric coupling coefficient, and an increased bandwidth.

The air edge 120, the air edge 130, and the air gap 140 may be emptyspaces, and thus may have substantially infinite impedance. Since theimpedance of the air edge 120, the air edge 130, and the air gap 140 aresubstantially infinite, an acoustic wave generated from the bulkacoustic wave resonance unit 110 may be reflected by a boundary surfaceof the air edge 120, the air edge 130, and the air gap 140, as opposedto being transferred to the air edge 120, the air edge 130, and the airgap 140.

The air edge 120 and the air edge 130 may be formed by etching apredetermined portion of an edge of the bulk acoustic wave resonanceunit 110 as thick as the bulk acoustic wave resonance unit 110 in avertical direction. The air edge 120 and the air edge 130 may be formedby etching a predetermined portion of an existing portion formed to bethe bulk acoustic wave resonance unit 110.

The air edge 120 and the air edge 130 are formed by penetrating apredetermined portion of the edge of the bulk acoustic wave resonanceunit 110. The air edge 120 and the air edge 130 may be connected to theair gap 140 to form an empty space.

The air edge 120 and the air edge 130 may be formed by layering aphoto-mask on a portion different from the edge of the bulk acousticwave resonance unit 110 and performing etching. Since a portion wherethe photo-mask is not layered is etched and thus, the first electrode115, the piezoelectric layer 113, and the second electrode 111 areetched in the same process at a given time and thus, steep slopes of theair edge 120 and the air edge 130 may be formed. Preferably, a steepslope of 90 degrees may be formed.

The air edge 120 and the air edge 130 may be formed by etching apredetermined portion of an edge of a portion where the first electrode115, the piezoelectric layer 113, and the second electrode 111 arelayered, as thick as the first electrode 115, the piezoelectric layer113, and the second electrode 111, in a vertical direction.

The edge of the bulk acoustic wave resonance unit 110 may be an areawhere a slope is formed on the bulk acoustic wave resonance unit 110.For example, the edge may correspond to a portion of the secondelectrode 111 having a different height as opposed to other portions ofthe second electrode 111, and an area where a slope begins.

The air edge 120 and the air edge 130 may be formed on a portion of theedge of the bulk acoustic wave resonance unit 110, preferably theportion being greater than or about equal to 20% of the edge.

The passivation layer 150 may be disposed on the substrate 160, and maybe disposed on or below the piezoelectric layer 113. The passivationlayer 150 may be disposed on or below the first electrode 115. Thepassivation layer 150 may be disposed on or below the second electrode111.

FIG. 2 illustrates a top view of an example of a BAWR in accordance withan illustrative example.

The BAWR of FIG. 2 is a top view of the BAWR of FIG. 1. The BAWR of FIG.1 is the cross-sectional view of the BAWR cut along a line 260.

The bulk acoustic wave resonance unit 210 includes a first electrode213, a second electrode 211, and a piezoelectric layer 240 between thefirst electrode 213 and the second electrode 211.

An air edge 220 and an air edge 230 may be formed on a portionpreferably greater than or equal to 20% of an edge of the bulk acousticwave resonance unit 210. Referring to FIG. 2, the air edge 220 and theair edge 230 may occupy about 60% of the edge. The air edge 220 and theair edge 230 may be formed on a portion excluding, from the edge, aportion where the first electrode 213 is connected and a portion wherethe second electrode 211 is connected.

An air gap may be disposed below the air edge 220, the air edge 230, andthe bulk acoustic wave resonance unit 210. The air gap may be disposedon a substrate 250.

A vertical acoustic wave generated in a direction from the secondelectrode 211 to the first electrode 213 may be reflected using the airgap as a reflector. A horizontal acoustic wave generated from the firstelectrode 213 and the second electrode 211 may be reflected using theair edge 220 and the air edge 230 as reflectors.

FIGS. 3A and 3B illustrate a top view and a sectional view of anotherexample of a BAWR in accordance with an illustrative example.

FIG. 3A illustrates the top view of the BAWR, and FIG. 3B illustratesthe sectional view of the BAWR cut along a line 301.

Referring to FIG. 3A, the BAWR includes a first electrode 311, a secondelectrode 313, a protective layer 315, a piezoelectric layer (not shown)disposed between the first electrode 311 and the second electrode 313,an air edge 321, and an air edge 323.

Dotted arrows in the protective layer 315 indicate that a horizontalacoustic wave generated from the BAWR is reflected through applicationof the air edge 321 and the air edge 323 as reflectors.

By way of non-limiting example, an air gap may be disposed below thefirst electrode 311. In this non-limiting example, a membrane (notshown) may be layered on the air gap to maintain a shape of the air gap.The air gap may be disposed on a substrate. In this non-limitingexample, a protective layer (not shown) may be layered on the substrateto prevent the substrate from being damaged during a process ofgenerating the air gap. The protective layer may be referred to as apassivation layer.

The air edge 321 and the air edge 323 may be generated by enlargingvia-holes (not shown). The air edge 321 and the air edge 323 may beformed by etching a portion of an edge of the BAWR.

The air edge 321 and the air edge 323 may be formed by penetrating anedge of a portion where the protective layer 315, the second electrode313, the piezoelectric layer (not shown), and the first electrode 311,up to the air gap in vertical direction.

Referring to FIG. 3B, the BAWR includes the first electrode 311, apiezoelectric layer 317, the second electrode 313, the protective layer315, a membrane 319, an air gap 330, the air edge 321, the air edge 323,a protective layer 340, and a substrate 350.

An RF signal may be input to the first electrode 311, and an RF signalmay be output from the second electrode 313. Conversely, an RF signalmay be input to the second electrode 313, and an RF signal may be outputfrom the first electrode 311.

The protective layer 315 may protect the second electrode 313 from beingexposed to an external side. Exposing the second electrode 313 to anexternal side may refer to being exposed to air, humidity, orenvironmental temperature or other factors.

The membrane 319 may be used to maintain a shape of the air gap 330. Theprotective layer 340 may be used to prevent the substrate 350 from beingdamaged during a process of generating the air gap 330. The protectivelayer 340 may be formed of one of silicon oxide-based material, asilicon nitride-based material, and an aluminum nitride-based materialor other suitable materials.

The air edge 321 and the air edge 323 may be formed by etching an edgeof a portion where the first electrode 311, the piezoelectric layer 317,the second electrode 313, the protective layer 315, and the membrane 319are layered. Also, the air edge 321 and the air edge 323 may be formedby enlarging via-holes (not shown) to be used for generating the air gap330.

A horizontal acoustic wave generated from the first electrode 311, thepiezoelectric layer 317, and the second electrode 313 may be reflectedthrough application of the air edge 321 and the air edge 323 asreflectors.

FIGS. 4A through 4C illustrate a top view and sectional views inaccordance with an illustrative example of a BAWR.

FIG. 4A is the top view of the BAWR including a bridge structure. FIG.4B is the sectional view of the BAWR cut along a line 401. FIG. 4C isthe sectional view of the BAWR cut along a line 403.

Referring to FIG. 4A, the BAWR includes a bridge 411 and a bridge 413.The bridge 411 and the bridge 413 correspond to portions where an airedge is not formed in an edge of the BAWR. A bridge indicates a portionthat is not etched in the edge of the BAWR. The structure of the BAWRmay be stably maintained through the bridge 411 and the bridge 413.

The bridge 411 and the bridge 413 may be disposed between air edges,respectively, on each side, to maintain shapes of the air edges.

Referring to FIG. 4B, the BAWR includes a protective layer 421, a secondelectrode 423, a piezoelectric layer 425, a first electrode 427, amembrane 429, an air gap 430, the bridge 411 and the bridge 413. Thebridge 411 and the bridge 413 may not be etched and support theprotective layer 421, the second electrode 423, the piezoelectric layer425, the first electrode 427, and the membrane 429 for the stability ofa physical structure.

Referring to FIG. 4C, the BAWR includes the protective layer 421, thesecond electrode 423, the piezoelectric layer 425, the first electrode427, the membrane 429, and the air gap 430, an air edge 431, and an airedge 433.

FIG. 5 illustrates a top view of in accordance with an illustrativeexample of a BAWR.

FIG. 5 illustrates the BAWR including an electrode in the form of afinger. The BAWR includes a first electrode 510, a second electrode 520,a piezoelectric layer disposed between the first electrode 510 and thesecond electrode 520, a protective layer 530, an air edge 541, an airedge 542, an air edge 543, an air edge 544, an air edge 545, and an airedge 546.

In this illustrative example, a predetermined portion patterned in theform of a finger included in the first electrode 510 may be etched. Inthis illustrative example, the air edge 542 and the air edge 543 may beformed on the etched predetermined portion.

Resistance is proportional to area. As an area of an electrodedecreases, a resistance of the electrode may decrease. Reflectivity isproportional to area. As an area of an air edge increases, areflectivity of a horizontal acoustic wave may increase.

Although the first electrode 510 includes three fingers in FIG. 5, thefirst electrode 510 may be configured to include a plurality of fingers.Here, the form of the finger describes that a predetermined area of thefirst electrode 510 is etched to be divided into a plurality ofportions, and a shape of the first electrode 510 divided into theplurality of portions may not be limited thereto.

A predetermined portion patterned in the form of a finger included inthe second electrode 520 may be etched. The air edge 545 and the airedge 546 may be formed on the etched predetermined portion.

Although the second electrode 520 includes three fingers in FIG. 5, thesecond electrode 520 may be configured to include a plurality offingers. In this illustrative example, the form of the finger describesthat a predetermined area of the second electrode 520 is etched to bedivided into a plurality of portions, and a shape of the secondelectrode 520 divided into the plurality of portions may not be limitedthereto.

An additional film (not shown) may be locally formed, throughevaporation, at a portion where the first electrode 510 and theprotective layer 530 are in contact and thus, a frame may be formed. Inthis illustrative example, the additional film may be formed of the samematerial as a material included in the protective layer 530. Further,the frame may be formed of a plurality of pieces of frames.

Also, an additional film (not shown) may be locally formed, throughevaporation, at a portion where the second electrode 520 and theprotective layer 530 are in contact and thus, a frame may be formed. Inthis illustrative example, the additional film may be formed of the samematerial as a material included in the protective layer 530.

A change in impedance may occur at a position where the frame is formedwhen the frame is additionally formed on the protective layer 530. Theimpedance of the BAWR may be determined based on the thickness oflayered films. Impedance may vary due to the change in thickness of thelayered films.

A horizontal acoustic wave generated from the first electrode 510 andthe second electrode 530 may be reflected using a surface where theframe is formed as a reflector based on a difference in impedance.

Furthermore, a U-shaped frame may be formed at a portion where the firstelectrode 510 and the protective layer 530 are in contact by locallyetching the protective layer 530.

Furthermore, a U-shaped frame may be formed at a portion where thesecond electrode 520 and the protective layer 530 are in contact bylocally etching the protective layer 530.

FIGS. 6A through 6C illustrate a top view and sectional views inaccordance with an illustrative example of a BAWR.

FIG. 6A is the top view of the BAWR when a frame is added. FIG. 6B isthe sectional view of the BAWR cut along a line 601. FIG. 6C is thesectional view of the BAWR cut along a line 603.

Referring to FIG. 6A, the BAWR includes a first electrode 611, a secondelectrode 613, and a protective layer 615, a piezoelectric layer (notshown) disposed between the first electrode 611 and the second electrode613, a frame 621, a frame 623, an air edge 631, and an air edge 633.

The frame 621 may be formed by locally forming, through evaporation, anadditional film at a portion where the first electrode 611 and theprotective layer 615 are in contact. In this illustrative example, theadditional film may be formed of the same material as a materialincluded in the protective layer 615. Further, the frame 621 may beformed of a plurality of pieces of frames.

The frame 623 may be formed by locally forming, through evaporation, anadditional film at a portion where the second electrode 613 and theprotective layer 615 are in contact. In this illustrative example, theadditional film may be formed of the same material as a materialincluded in the protective layer 615. Further, the frame 623 may beformed of a plurality of pieces of frames.

A horizontal acoustic wave generated from the first electrode 611 andthe second electrode 613 may be reflected using a surface where theframe 621 is formed and a surface where the frame 623 is formed, asreflectors based on different impedances.

Referring to FIG. 6B, the BAWR includes the first electrode 611, apiezoelectric layer 617, the second electrode 613, the protective layer615, the frame 621, the frame 623, a membrane 609, an air gap 619, aprotective layer 640, and a substrate 650.

A thickness of the frame 621 and a thickness of the frame 623 aredifferent from the thicknesses of remaining portions of the frames.Accordingly, a horizontal acoustic wave generated from the firstelectrode 611 and the second electrode 613 may be reflected using asurface where the frame 621 is formed and a surface where the frame 623is formed, as reflectors based on a difference in impedances.

Referring to FIG. 6C, the BAWR includes the first electrode 611, thepiezoelectric layer 617, the second electrode 613, the protective layer615, an air edge 631, an air edge 633, the membrane 609, the air gap619, and the protective layer 640, and the substrate 650.

The air edge 631 and the air edge 633 may be empty spaces and may havean infinite value of impedance. A horizontal acoustic wave generatedfrom the first electrode 611 and the second electrode 613 may bereflected using a surface where the air edge 631 is formed and a surfacewhere the air edge 633 is formed, as reflectors based on a difference inimpedances.

FIGS. 7A through 7C illustrate a top view and sectional views inaccordance with an illustrative example of a BAWR.

FIG. 7A is the top view of the BAWR when a U-shaped frame is formed.FIG. 7B is the sectional view of the BAWR cut along a line 701. FIG. 7Cis the sectional view of the BAWR cut along a line 703.

When compared to the BAWR of FIG. 6, the BAWR of FIG. 7 may include aframe 721 and a frame 723 that are formed based on a different schemefrom that which was previously disclosed herein.

Referring to FIG. 7A, the frame 721 may be formed in a shape of U bylocally etching a protective layer at a portion where a first electrodeand the protective layer are in contact.

The frame 723 may be formed in a U shape by locally etching theprotective layer at a portion where a second electrode and theprotective layer are in contact.

A total thickness of films layered at a portion where the frame 721 isdisposed and a total thickness of films layered at a portion where theframe 723 is disposed are less than thicknesses of remaining portions ofthe frames. Thus, a difference in impedance may occur due to adifference in the thicknesses of the films.

A horizontal acoustic wave generated from the first electrode and thesecond electrode may be reflected using a surface where the frame 721 isformed and a surface where the frame 723 is formed, as reflectors basedon an impedance difference.

Referring to FIG. 7B, a thickness of films layered at a portion wherethe frame 721 is disposed and a thickness of films layered at a portionwhere the frame 723 is disposed may be less than thicknesses ofremaining portions of the frames.

Referring to FIG. 7C, the BAWR may include an air edge, like the BAWR ofFIG. 6C. A horizontal acoustic wave generated from the first electrodeand the second electrode may be reflected using a surface where an airedge is formed and a surface where an air edge is formed, as reflectorsbased on an impedance difference.

FIG. 8 is a flow chart illustrating a method of manufacturing a BAWRunit in accordance with an illustrative example.

Referring to FIG. 8, at 810, the method forms the first electrode 115 ofFIG. 1, by way of illustration, at 820 the method forms a piezoelectriclayer 113 between the first electrode 115 and a second electrode 111 at830. At 840, the method forms an air edge 120 or an air edge 130.

The units described herein may be implemented using hardware componentsand software components. For example, microphones, amplifiers, band-passfilters, audio to digital convertors, and processing devices. Aprocessing device may be implemented using one or more general-purposeor special purpose computers, such as, for example, a processor, acontroller and an arithmetic logic unit, a digital signal processor, amicrocomputer, a field programmable array, a programmable logic unit, amicroprocessor or any other device capable of responding to andexecuting instructions in a defined manner. The processing device mayrun an operating system (OS) and one or more software applications thatrun on the OS. The processing device also may access, store, manipulate,process, and create data in response to execution of the software. Forpurpose of simplicity, the description of a processing device is used assingular; however, one skilled in the art will appreciated that aprocessing device may include multiple processing elements and multipletypes of processing elements. For example, a processing device mayinclude multiple processors or a processor and a controller. Inaddition, different processing configurations are possible, such aparallel processors.

A number of illustrative examples have been described above.Nevertheless, it should be understood that various modifications may bemade. For example, suitable results may be achieved if the describedtechniques are performed in a different order and/or if components in adescribed system, architecture, device, or circuit are combined in adifferent manner and/or replaced or supplemented by other components ortheir equivalents. Accordingly, other implementations are within thescope of the following claims.

What is claimed is:
 1. A film bulk acoustic wave resonator (BAWR),comprising: a resonance unit comprising a first electrode, a secondelectrode, and a piezoelectric layer disposed between the firstelectrode and the second electrode; an air gap disposed below theresonance unit; and an air edge provided distant from a center of theresonance unit to interface with the air gap before an edge of the airgap, wherein the air gap is configured to reflect acoustic waves of theresonance unit in a vertical direction and the air edge is configured toreflect acoustic waves of the resonance unit in a horizontal direction.2. The BAWR of claim 1, wherein the air edge partially surrounds theresonance unit.
 3. The BAWR of claim 2, wherein the air edge partiallysurrounds more than 20% of the resonance unit.
 4. The BAWR of claim 3,further comprising an additional air edge, where the air edge and theadditional air edge together surround at least 60% of the resonanceunit.
 5. The BAWR of claim 1, further comprising an additional air edge,with the air edge and the additional air edge partially surrounding theresonance unit.
 6. The BAWR of claim 5, further comprising a framealigned over an outer portion of the first electrode in the resonanceunit.
 7. The BAWR of claim 5, further comprising a frame, aligned overan outer portion of the first electrode in the resonance unit, etched ina form of a finger.
 8. The BAWR of claim 5, wherein the second electrodecomprises: a portion in a form of a finger, in contact with a portion ofthe resonance unit; and a patterned portion exposed to the air edge. 9.The BAWR of claim 5, wherein the air edge is formed in the verticaldirection.
 10. The BAWR of claim 5, wherein the resonance unit furthercomprises a membrane disposed above the air gap that maintains a shapeof the air gap.
 11. The BAWR of claim 1, wherein the air gap is disposedon a substrate.
 12. The BAWR of claim 11, wherein the air edge is formedin the vertical direction.
 13. The BAWR of claim 11, wherein theresonance unit further comprises a membrane disposed above the air gapand maintains a shape of the air gap.
 14. The BAWR of claim 1, whereinthe air edge is an enlargement of a via-hole that was used to generatethe air gap.
 15. The BAWR of claim 14, wherein the air edge partiallysurrounds the resonance unit.
 16. The BAWR of claim 15, wherein the airedge partially surrounds more than 20% of the resonance unit.
 17. TheBAWR of claim 16, further comprising an additional air edge, with theair edge and the additional air edge surrounding about 60% of theresonance unit.
 18. The BAWR of claim 14, wherein the air edge is formedin the vertical direction.
 19. The BAWR of claim 14, wherein theresonance unit further comprises a membrane disposed above the air gapand maintains a shape of the air gap.
 20. The BAWR of claim 14, whereinthe first electrode, the second electrode, and the piezoelectric layerare etched in a single process, through application of a photo-masklayered on a portion different from an edge of the resonance unit sothat the air edge has a steep slope.
 21. The BAWR of claim 14, furthercomprising a frame aligned over an outer portion of the first electrodein the resonance unit.
 22. The BAWR of claim 14, further comprising aframe, aligned over an outer portion of the first electrode, etched in aform of a finger.
 23. The BAWR of claim 14, wherein the second electrodecomprises: a portion in a form of a finger, in contact with a portion ofthe resonance unit; and a patterned portion exposed to the air edge. 24.The BAWR of claim 1, wherein the first electrode, the second electrode,and the piezoelectric layer are etched in a single process, throughapplication of a photo-mask layered on a portion different from an edgeof the resonance unit so that the air edge has a steep slope.
 25. TheBAWR of claim 1, further comprising a frame aligned over an outerportion of the first electrode in the resonance unit.
 26. The BAWR ofclaim 1, wherein the air edge is an etched portion of the BAWR throughrespective portions of the first electrode, the piezoelectric layer, andthe second electrode.
 27. A film bulk acoustic wave resonator (BAWR),comprising: a resonance unit comprising a first electrode, a secondelectrode, and a piezoelectric layer disposed between the firstelectrode and the second electrode; and an air edge provided distantfrom a center of the resonance unit, wherein the first electrodecomprises: a portion in a form of a finger, in contact with a portion ofan edge of the resonance unit; and a patterned portion exposed to theair edge.
 28. A film bulk acoustic wave resonator (BAWR), comprising: anair gap; a resonance unit comprising a first electrode disposed abovethe air gap, a piezoelectric layer disposed above the first electrode,and a second electrode disposed above the piezoelectric layer; andplural air edges formed at a distance from a center of the air gap andrespectively interfacing with the air gap before an edge of the air gap,wherein the plural air edges are configured to control acoustic wavereflectivity of the resonance unit.
 29. The BAWR of claim 28, furthercomprising a substrate, wherein the air gap is formed on the substrate.30. The BAWR of claim 28, wherein the plural air edges include an airedge as an etched portion through respective portions, outside of theresonance unit, of the first electrode, the piezoelectric layer, and thesecond electrode.